(1) Field of the Invention
The present invention relates to a film-forming method for an X-ray mask and an apparatus for carrying out the film-forming method in which a film-forming can be accomplished such that a stress in an X-ray absorber of an X-ray mask for use in X-ray lithography is decreased everywhere to zero or to a negligible degree.
(2) Description of the Related Art
FIG. 30 is a sectional view showing a construction of a conventional film-forming apparatus for a X-ray mask with a stress distribution attained thereby. In FIG. 30, a X-ray absorber 2 is formed on a mask substrate 1. A target 3 is attached to a front surface of a magnet 4 for stabilizing an electric discharge and arranged opposite to the mask substrate 1.
Conventionally, as shown in FIG. 30, the X-ray absorber 2 is formed as a film on the mask substrate 1 by means of sputtering of the target 3. Using this method, a stress distribution in the X-ray absorber 2 will have a compressive stress which is high at a mid portion and reduced toward opposite ends, because the intensity of plasma gets stronger toward the mid portion of the target 3.
In the conventional stress distribution, a desirable stress distributing range is defined by a range represented by "a" in which a stress variation is included within a position range of "b" and which is located at the mid portion having less stress variation. Thus the X-ray absorber 2 is formed with a film formed only in the "a" range. Therefore, there is a problem that a film-forming range is limited due to the increase in an ineffective area and corresponding low productivity.
For solving such a problem, in the Japanese Patent Application No. 8-154322, we have already proposed a method for having a uniform a stress distribution in the X-ray absorber by means of annealing. One example of this method is illustrated in FIG. 31. First, a hot-plate 60 having a plurality of heaters 61a, 61b, 61c embedded therein is provided for controlling a temperature distribution of its working surface. FIG. 32A shows a measured stress distribution in the X-ray absorber 2. Annealing in an X-ray absorber 2 distributes the stress at the rate of about 1 MPa per 1.degree. C. toward a tensile stress side, so that the annealing is carried out according to a temperature distribution on the hot-plate 60 as shown in FIG. 32B based on calculation of the stress distribution where all of the stress become zero.
In such an annealing method, even if the X-ray absorber 2 is formed in a range wider than the "a" range shown in FIG. 30, when the temperature distribution in the hot-plate 60 is adequately set, it becomes possible to eliminate the stress unevenness and to make the stress zero. Therefore, this annealing method provides such a superior feature that the stress and its unevenness can be made zero even if a film-forming apparatus or a film-forming method would be not optimized.
However, there are still remains the following problems;
1) Such a forming method is not suitable for mass production because a stress measurement, a temperature setting and so on are required for every absorber 2 at the time of annealing. PA1 2) When the mask substrate 1 to be formed has an increased thickness, it becomes difficult to provide an adequate temperature distribution to make the stress unevenness zero because the mask substrate 1 itself has good thermal conduction which make it difficult to have proper temperature distribution. PA1 1) at least one third gear is interposed between a first gear having its axis coincident with the revolving center of the mask substrate and a second gear having its axis coincident with the rotating center thereof so that a distance between a center of the first gear and a center of the second gear can be changed through the third gear. PA1 2) a first gear having its axis coincident with the revolving center of the mask substrate, a second gear having its axis coincident with the rotating center thereof, a third gear meshing with the first gear and a belt for connecting the third gear and the second gear are arranged in a manner that a distance between a center of the first gear and a center of the second gear can be changed through the third gear and the belt. PA1 3) a first gear having its axis coincident with the revolving center of the mask substrate and a second gear having its axis coincident with the rotating center thereof are connected by at least one belt in a manner that a distance between a center of the first gear and a center of the second gear can be changed by extending and contracting the belt.